The invention relates to a system and method for controlling fuel vapor purging in a vehicle equipped with an internal combustion engine coupled to a fuel tank coupled to a purging canister.
Vehicles typically have various devices installed for preventing and controlling emissions. One of the sources of emissions are fuel vapors generated in the fuel tank due to temperature cycling and fuel vapors that are displaced in the process of refueling the fuel tank. In order to remove these vapors from the fuel tank, vehicles are equipped with fuel emission control systems, typically including a fuel vapor storage device, which in this example is an activated charcoal filled canister for absorbing the evaporative emissions. One such system is described in U.S. Pat. No. 5,048,492, where a three way connection between the fuel tank, the canister and the engine is established. The engine is connected to the fuel tank and the carbon canister via a communication passage. Vapors generated in the fuel tank are drawn into the canister where the fuel component (usually hydrocarbons) is absorbed on the carbon granules, and the air is expelled into the atmosphere. A purge control valve is located in the intake manifold of the engine. A controller selectively opens and closes the purge control valve to allow purged fuel vapors to enter the engine.
The inventors herein have recognized a disadvantage with the above approaches, namely, there is a risk of rich or lean spikes or air and fuel vapors inducted into the engine during canister purging since the tank is not isolated. These vapor transients can cause vehicle stalls or degrade emission control. Under certain conditions, with the vapors from the fuel tank always entering the canister, the rate of fuel vapor generation may become greater than the rate of purge into the engine. Also, with this configuration, it is not possible to accurately estimate the amount of fuel vapor entering the engine and therefore not possible to accurately adjust the fuel injection strategy in response to additional fuel entering the engine as a result of fuel vapor purging.
An object of the present invention is to provide a system for improved control of fuel vapor purging into internal combustion engine, and to develop better estimates of engine operating conditions based on the improved control methodology.
The above object is achieved and disadvantages of prior approaches overcome by a method for controlling an internal combustion engine in a vehicle having a fuel purge control system having a fuel vapor storage device, a fuel tank, a purge control valve and a tank control valve. The method includes the steps of: estimating a fuel fraction coming from the fuel vapor storage device into the engine when the fuel tank is isolated from the engine and from the canister; and adjusting an engine parameter based on said estimated fuel fraction.
An advantage of the above aspect of the invention is that the proposed system configuration allows isolating the fuel tank during canister purging and therefore prevents fuel vapor spikes into the engine. With the tank isolated, the characteristics of the carbon canister can be more reliably modeled, and better estimates of the fuel fraction in the flow into the engine through the purge valve (out of the canister) can be achieved. This information in turn can be used to provide more accurate feed forward adjustments to the fuel injectors. In other words, having a better estimate of the fuel fraction coming out of the canister during the canister purge will allow better control of the air/fuel system, thus improving fuel efficiency and emissions. Another advantage is the proposed configuration purge time will be reduced due to the fact that fuel tank vapors will not continuously be entering the canister.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.